The major objective of this project concerns the elucidation of the role of singlet oxygen - O2 ('delta g) - in physiological environments. To this end we have applied the technique of pulsed laser flash photolysis for generating O2 ('delta g) by energy transfer from various sensitizer molecules. The dynamics of the reactions of singlet oxygen with various biologically important residues has been determined by kinetic spectrophotometry with nanosecond time resolution. Dispersion systems such as aqueous micelles, reverse micelles and vesicles have been employed. These are formed by aggregation of surface-active materials in fluid solutions and offer the opportunity of using well-defined micro-heterogenous phases in which to stuy the reaction parameters. In this way the complex biological environments are effectively mimicked. With these techniques the natural lifetime of the O2 ('delta g) molecule in pure water, micellar media and vesicles have been determined along with the biomolecular rate constants for several substrates of biological import. Further, an approach to the question of whether O2 ('delta g) is capable of participatng in electron transfer reactions has been undertaken.